In the manufacture of paper products, particularly tissue products, it is generally desirable to provide an aesthetically pleasing final product with as much bulk as possible without compromising other product attributes, including softness, flexibility, absorbency, hand feel, and durability. However, most papermaking machines operating today utilize a process known as “wet-pressing”. In “wet-pressing” a large amount of water is removed from the newly-formed web of paper by mechanically pressing water out of the web in a pressure nip. A disadvantage of the pressing step is that it densifies the web, thereby decreasing the bulk and absorbency of the sheet. One problem encountered in the past by first wet web pressing and/or then dry embossing is the difficulty in obtaining a tissue basesheet with good functionality, such as absorbency and softness, in combination with a pleasant appearance. This wet-pressing step, while an effective dewatering means, compresses the web and causes a marked reduction in web thickness, thus reducing bulk. In addition, using embossing to apply signature designs to a dry web generally results in a paper product that is gritty to hand feel, stiffer at the pattern edges, and with decreased absorbency.
Alternatives to wet-pressing such as through-air drying generally subject the web to less compression during manufacturing. For example, through-air drying typically involves forming a wet web from papermaking furnish on a forming media, such as a forming fabric or wire. Then, the wet web is transferred to a permeable through-air-drying fabric around an open drum and non-compressively dried by passing hot air through the web while in intimate contact with the fabric. Throughdrying is a preferred method of drying a web because it avoids the compressive force of the dewatering step used in the conventional wet press method of tissue making. The resulting web optionally may be transferred to a Yankee dryer for creping. Such processes are typically referred to as creped through-air dried (CTAD). Because the web is substantially dry when transferred to the Yankee dryer, the process does not densify the sheet as much as the wet press process, however, embossing may still be needed to provide a tissue product having consumer preferred sheet bulk and designs. As with wet pressed webs, embossing has the drawback of a product that is gritty to hand feel, stiffer at the pattern edges, and with decreased absorbency.
An alternative to CTAD is the uncreped through-air dried (UCTAD) process described in U.S. Pat. Nos. 5,591,309 and 5,593,545. By eliminating the creping step the resulting web has relatively high bulk, good compressibility, and high resiliency, with the attendant benefits of increased absorbency and improved fiber utilization. While the webs improved bulk and resiliency may be desirable traits from a consumer perspective, they make the web difficult to emboss. Often patterns imparted to an UCTAD web by conventional embossing are poorly defined and fade over time as the bulk and resilient web relaxes.
Because it is poorly suited to embossing, tissue makers wishing to create UCTAD webs with design motifs have often resorted to using patterned through-air drying fabrics. For example, U.S. Pat. Nos. 6,749,719 and 7,624,765 disclose fabrics useful in the formation of tissue webs having design elements using the UCTAD process. While these fabrics may provide webs having design elements, they also impart the web with an overall textured background pattern. Thus, it may be difficult to discern the design elements. Further, the addition of design elements to the through-air drying fabrics reduces their air permeability, which in-turn reduces manufacturing efficiency.
Accordingly, there remains a need in the art for imparting textured webs with a design element and more specifically a need for imparting designs on through-air dried webs without negatively affecting the web's physical properties or the efficiency with which the webs are manufactured.